Sprinkle flour "just before" you put the prawns on the frying pan. The flour helps making the skin turning golden brown.

Melt the butter and little olive oil in a medium to large frying pan on medium-high heat. Add the prawns first on one side for about 1 minute, then add the garlic. Do not stir the prawns (instead just move the pan over the fire) until you see color starts to change then turn to the other side. Sprinkle herbs. Serve hot.